For a liquid crystal display apparatus including a liquid crystal panel that modulates light-source light in accordance with a video signal and a light source such as a backlight for applying light to the liquid crystal panel, technologies have been proposed to improve quality of display video by controlling the emission luminance of the backlight light source depending on a video signal.
For example, a patent document 1 and a patent document 2 have proposed those capable of displaying high-quality moving picture with sharp contrast (with dynamic contrast augmented) by detecting an average picture level (APL) as a feature quantity of an input video signal, reducing the emission luminance when the detected average picture level is high, and increasing the emission luminance when the level is low to differentiate the screen luminance even though the video is displayed at the same gradation level and dynamically change the screen luminance depending on displayed video contents.
With regard to such a technology that uses a feature quantity of an input video signal to control the emission luminance of the backlight light source, for example, Japanese Patent Application No. 2005-39959 (filed on May 6, 2004) filed by the same applicant as that of the present application describes an image display device capable of reducing effects of undesirable additional information as much as possible to constantly acquire the optimum screen luminance. This image display device includes a liquid crystal panel that uses a backlight light source to display an input video signal, a feature-quantity detecting means that detects a feature quantity of an input video signal, and a light-source controlling means that dynamically and variably controls the emission luminance of the backlight light source based on the feature quantity detected by the feature-quantity detecting means.
The feature-quantity detecting means extracts a video signal of a predetermined area in a screen to detect a feature quantity of the extracted video signal. This enables the effects of the undesirable additional information included in the input video signal to be reduced as much as possible to acquire the optimum screen luminance (brightness) depending on original video contents.
Patent Document 1: Japanese Laid-Open Patent Publication No. 8-201812
Patent Document 2: WO03/38799